The present invention relates to a method for preparing a new flame-retardant triallyl isocyanurate prepolymer having a relatively low molecular weight.
Triallyl isocyanurate (referred to as "TAIC" hereinafter) is a chemical compound also called chemically triallyl ester of isocyanuric acid or allyl isocyanate trimer and is also a tautomer of triallyl cyanurate. Since TAIC is superior in chemical and thermal stability to the latter, it has attracted special interest recetly as a vinyl monomer which can be used as a crosslinking agent for various thermosetting resins and synthetic rubbers or a modifier for their thermal resistances, mechanical properties, hydrolysis resistances and the like.
Although it is widely practised that TAIC is added in a form of monomer to various synthetic resins or rubbers to be modified to crosslink them, it is often used in a form of prepolymer of relatively low molecular weight depending on the applications including electronic materials, synthetic resins, paints, adhesives and other industrial materials, as described, for example, in Japanese Laid-Open Patent Publications No. 74245 of 1981 and No. 16911 of 1986. In these applications, flame retardancy is firmly required. Accordingly, the development of a flame-retardant TAIC prepolymer is of high industrial importance.
Various methods for the preparation of a TAIC prepolymer have been proposed. For example, Japanese Patent Publication No. 26586 of 1963 and Japanese Laid-Open Patent Publication No. 54192 of 1973 disclose a method of reacting TAIC with an aliphatic aldehyde having 2 to 8 carbon atoms in the presence of a polymerization initiator. However, the TAIC prepolymer prepared by this method shows no flame retandancy and the final product tends to discolor on standing.
Japanese Laid-Open Patent Publication No. 77294 of 1978 describes a method for the preparation which improves improving in yield and purity and in which the solid TAIC prepolymer is separated and then the methylcarbonylpropyl group containing residue included in the mother liquor is recovered for use. Even this method cannot solve the above problem. Further, it is disadvantageous for industrial manufacturing because of requiring an autoclave as the reactor.
On the other hand, as a method for flame retarding the TAIC prepolymer, Japanese Laid-Open Patent Publication No. 198739 of 1982 describes that diallyl tetrabromophthalate is used as a reactive flame retarding agent to the TAIC-diallyl phthalate copolymerized prepolymer. This method lowers the content of TAIC moiety naturally and thus the deterioration of physical properties possessed originally by TAIC cannot be avoided.
Furthermore, a method is well known in which, as a method for the preparation of a flame retardant prepolymer having a low molecular weight, TAIC is polymerized in a halogenated hydrocarbon and a segment of the solvent is combined to the prepolymer molecule by utilizing the chain transfer reaction to the solvent in order to synthesize a halogenated TAIC prepolymer. According to the inventors' tracing, however, not only a colored product was prepared but also the lowering of molecular weight, that is, the chain transfer effect, was insufficient when the selected halogenated hydrocarbon was not suitable and, in some cases it inhibited the polymerization reaction. Accordingly, this method is also unsuitable as the method for the preparation of a TAIC prepolymer of high quality.
Therefore, the primary object of the invention is to solve the above problems and to provide a method for industrial preparation of a flame retardant TAIC prepolymer which has not only excellent flame retardancy but also good physical properties.